Power steering system

ABSTRACT

A power steering system for a motor vehicle which in its presently preferred embodiment has a power steering gear, a steering wheel, and a steering shaft connecting the wheel to the steering gear. A spiral leaf spring is connected to the steering shaft and exerts a force tending to center the steering wheel and shaft.

United States Patent Van Wicklin, Jr. 51 Jan. 25, 1972 I POWER STEERINGSYSTEM [56] References Cited [72] Inventor: W lrren A. Van Wlcklln, Jr.,Dearbom. UNITED STATES TENTS l,383,348 7/1921 Stanbon ..74/495 1 n FordMotor m yJ m 3,374,850 3/1968 Cech ..74 4o5x 221 Filed: Dec. 11,1968

[2i] Appl. No.: 782,948

[51] lnt.Cl [58] Field of Selrch.....

Primary Examiner-Milton Kaufman Attorney-John R. Faulkner and CliffordL. Sadler [57] ABSTRACT A power steering system for a motor vehiclewhich in its presently preferred embodiment has a power steering gear, asteering wheel, and a steering shaft connecting the wheel to thesteering gear. A spiral leaf spring is connected to the steering shaftand exerts a force tending to center the steering wheel and shaft.

2 Claims, 4 Drawing Figures POWER STEEG SYSTEM BACKGROUND OF THEINVENTION Two principal types of power steering reaction, or means ofproviding feel, have been used in passenger cars. l-listori cally, thefirst approach was the use of hydraulic reaction. In this system ahydraulic reaction area is provided on the hydraulic servocontrol valve.The hydraulic pressure that is furnished to the power cylinder also actsupon the hydraulic reaction area, producing a reaction forceproportional to the amount of power boost.

This construction provided a linear relationship between the reactionforce (steering efiort) and output torque. In the early period of powersteering, this linear relationship was favored. The characteristics ofhydraulic reaction arezl) light steering efl'ort for correctivesteering, 2) good recovery action, 3) relatively high parking efiortsince the output torque at parking is about three times greater than forcornering with the steering effort correspondingly greater, and 4) amoderate amount of feedback from road disturbances to the front wheels.

As the demand for lower steering effort increased, the use of hydraulicreaction was extended by the addition of a pressure reducing valve tocontrol the hydraulic pressure acting upon the reaction area. Thisvalve, sometimes known as a parking valve, provides linear reactionduring corrective steering and cornering but then limits the reactionpressure as the output torque increases above that encountered incomering. This gives the designer additional freedom in establishing therelationship between steering efiort and output torque.

Another development in producing and controlling steering effort inpower steering systems is torsion spring reaction, such as disclosed inU.S. Pat. No. 3,292,499 issued Dec. 20, 1966 to James J. Duffy. Themetering of the control valve is designed to produce a pressure outputacross the power cylinder proportional to the square of the valvedisplacement. The deflection of the torsion spring is proportional tothe steering effort. This results in the output torque beingproportional to the square of the steering effort. Characteristics oftorsion spring reaction are: I) light steering effort for correctivesteering, 2) fair recovery, 3) moderate parking efi'ort, 4) low feedbackfrom road disturbances.

In each of these two approaches, the designer is restrained by somerelationship between corrective steering effort, recovery, feedback andparking efiort so that he cannot control these factors independently.

BRIEF SUMMARY OF THE DISCLOSURE In view of the state of the art theobjective of this disclosure is to present a construction which provideslowsteering effort, outstanding recovery and elimination of feedback.This is accomplished by imposing a spring produced centering torque uponthe steering shafi and eliminating or minimizing all other reactiontorques.

The presently preferred embodiment provides a spiral leaf spring that ismounted on the steering column housing and is connected to the steeringshaft. The system includes a power steering gear constructed to haveminimal reaction torque, i.e., it requires minimum input effort toobtain the desired output responses to efiect a steering maneuver. Thespiral leaf spring is constructed to provide the steering effort whichthe driver experiences and the torque to return the steering shaft toits center or neutral position.

Rotation of the steering shaft from the straight-ahead position causesthe steering effort to increase rapidly, giving a positive center feel.Further rotation of the steering shaft, as during cornering, results invery little added steering efiort since the torsional rate is reduced asthe angular deflection increases. This results from the peculiardeflection versus spring rate characteristics of a spiral leaf spring.The torsional rate drops to approximately zero at one revolution of thesteering shaft from the straight-ahead position so there is almost noincrease in steering effort as the front wheels are turned to the limitsof their travel.

BRIEF DESCRIPTION OF THE DRAWINGS The many objects and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description and the accompanying drawings in which:

FIG. 1 is a side elevational view of a portion of a power steeringsystem incorporating the present invention;

FIG. 2 is an enlarged elevational view partly in section of the steeringshaft centering device of this invention;

FIG. 3 is an end view partly section of the device of FIG. 2; and

FIG. 4 is a steering effort versus steering wheel position curve for atypical steering system incorporating the present invention.

DETAILED DESCRIPTION OF Til-IE PREFERRED EMBODIMENT Referring now to thedrawings wherein the presently preferred embodiment of the invention isdisclosed, FIG. 1 shows a portion of a power steering system for a motorvehicle. The system of FIG. 1 includes a steering column assembly 10having a stationary steering column housing 14 that rotatably supports asteering shaft 12. An instrument panel 16 of a vehicle having thissystem supports the housing 14. A steering wheel 18 is connected to theupper end of the steering shaft 12 and is positioned to be rotated bythe vehicle operator.

A power steering gear 20 is connected to the lower end of the shaft 12.The power steering gear 20 may be of the type illustrated in US. Pat.No. 3,292,499 issued to James J. Duffy on Dec. 20, 1966. The steeringgear 20 constructed to be connected to the steering linkage system forthe front steerable wheels of the vehicle. A power steering pump 21 isarranged to be driven by the vehicle engine. A flexible hose conveyshydraulic fluid under pressure from the pump 19 to the power steeringgear 20.

A centering device 22 is supported on the steering column and isconstructed to maintain the steering shaft 12, the steering wheel 18 andthe steerable road wheels of the vehicle in a center or a neutralposition. The device 22 includes a housing 24 that is connected to thetubular housing 14 of the steering column by means of a pair of bolts 26and 28 as seen in FIG. 3. The housing 24 is bored to receive a bearing30 and the bearing, in turn, rotatably supports a shaft 32.

As seen in FIG. 2, a spool 34 is secured to the left side of the shaft32. A spiral leaf spring 36 is secured to the right-hand protruding endof the shaft 32. The inner end 38 of the leaf spring 36 is secured in aslot 40 formed in the shaft 32. The spring 36 is enclosed in a stampedhousing 42 which, in turn, is secured to the housing member 24 of theassembly 22 by means of bolts 43. The outer end of the spring 36 isriveted at 44 to the housing 42.

A spool having semicylindrical parts 46 and 48 is secured to thesteering shaft 12 by means of cap screws 50. A flexible cable 52 has itsmidportion secured to the spool 34 mounted on shaft 32. The free ends 54and 56 of the flexible cable 52 are connected to the spool parts 46 and48, respectively, by

retaining pins 58 and 60. It will be noted from FIG. 3 that the cable 52is secured to the spool 34 and wound about it in such a manner that bothof the free ends 54 and 56 come off of the spool on the same side.

As seen in FIG. 3,, the free ends 54 and 56 of the cable 52 form anangle. When the vehicle's front wheels are in a neutral straight-aheadposition, the retaining pins 58 and 60 are situated relative to theshaft 12 so that the bisector of the angle formed by the free ends 54and 56 extends through the center of the shaft 12. The shaft 12 is thencentered in its neutral position.

In a power steering system having the centering device of FIGS. 2 and 3,the power steering gear 20 is constructed to have minimum reactiontorque. A distinctive characteristic of this invention is that thesteering effort is only a function of the steering angle and not afunction of the output torque of the power steering gear 20. Therefore,the steering effort evidenced at the steering wheel by the driver is notdependent upon the type of road surface. lce covered roads give the samepositive power feel as dry pavement.

This unique construction makes it possible to realize certain economiesin the construction of the control valve within the power steering gearwithout impairing the quality of the performance of the power steeringsince the valve metering characteristics no longer must be controlled toachieve the desired steering efiort.

Recovery after executing a steering maneuver is independent from theself-aligning torque of the pneumatic tires. Power recovery is furnishedat all times even when the vehicle is at rest. The recovery is poweredrecovery because the spring 36 drives the power steering gear 20 throughthe shaft 12. The recovery is always uniform and is unaffected byvehicle speed and attitude.

In a power steering system in accordance with this invention and havinga power steering gear of the general type described in U.S. Pat. No.3,292,499, the torsion bar of the steering gear may be reduced to have adiameter of only one-tenth of an inch. This reduces the torsional rateof the torsion bar within the steering gear to one-sixth of the normalrate. Because the rate of the torsion bar is so greatly reduced, the barfunctions mainly as a column or positioning member to locate the inputshaft in its proper axial position, Pretensioning of the spiral spring36 permits adjustment of the initial steering effort rate. As thesteering wheel is rotated from straight-ahead position, the retractorspring is extended. Since this spring is almost a constant force device,the steering efiort versus steering wheel position relationship isestablished as shown in FIG. 4. in that figure, a curve for a typicalinstallation of the present invention is illustrated.

CONCLUSION Therefore, the present invention provides a constructionhaving a power steering system characterized by low-steering effort,outstanding recovery and elimination of feedback. This object isaccomplished by providing a spring produced centering torque to thesteering shaft and eliminating or minimizing all other reactions torque.The force exerted by the spring 36 upon the shaft 12 exceeds any otherreaction torque that may exist in the system.

I claim:

1. A power steering system for a motor vehicle having a power steeringgear, a hydraulic pressure source connected to said gear, a steeringshaft, a steering column assembly rotatably supporting said shaft, saidshaft having one end connected to said steering gear and its other endconnected to a steering wheel, a spring device supported on saidsteering column assembly, said device having rotatably mounted shaftspaced from said steering shaft, a spiral leaf spring having one endconnected to said second-mentioned shaft, the other end of said springbeing anchored on said steering column assembly, a spool connected tosaid second mentioned shaft, flexible connecting means interconnectingsaid spool and said steering shaft whereby when said steering shaft isrotated a spring force is transmitted from said spiral leaf springthrough said flexible connecting means to said steering shaft tending tourge said steering shaft to its central neutral position.

2. A power steering system for a motor vehicle having a power steeringgear, a hydraulic pressure source connected to said gear, a steeringshaft, a steering column assembly rotatably supporting said shaft, saidshaft having one end connected to said steering gear and its other endconnected to a steering wheel, a spring device supported on aid steeringcolumn assembly, said device having a rotatably mounted shaft spacedfrom said steering shaft, a spiral leaf spring having one end connectedto said second-mentioned shaft, the

other end of said spring being anchored on said steering columnassembly, a spool connected to said second-mentioned shaft, flexibleconnecting means interconnecting said spool and said steering shaftwhereby when said steering shaft is rotated a spring force istransmitted from said spiral leaf spring through said flexibleconnecting means to said steering shaft tending to urge to steeringshaft to its central neutral position, said spring device exerting aforce on said steering shaft when said steering shaft is turned to anonneutral position that exceeds any reaction force occurring in saidsteering gear.

1. A power steering system for a motor vehicle having a power steeringgear, a hydraulic pressure source connected to said gear, a steeringshaft, a steering column assembly rotatably supporting said shaft, saidshaft having one end connected to said steering gear and its other endconnected to a steering wheel, a spring device supported on saidsteering column assembly, said device having a rotatably mounted shaftspaced from said steering shaft, a spiral leaf spring having one endconnected to said second-mentioned shaft, the other end of said springbeing anchored on said steering column assembly, a spool connected tosaid second mentioned shaft, flexible connecting means interconnectingsaid spool and said steering shaft whereby when said steering shaft isrotated a spring force is transmitted from said spiral leaf springthrough said flexible connecting means to said steering shaft tending tourge said steering shaft to its central neutral position.
 2. A powersteering system for a motor vehicle having a power steering gear, ahydraulic pressure source connected to said gear, a steering shaft, asteering column assembly rotatably supporting said shaft, said shafthaving one end connected to said steering gear and its other endconnected to a steering wheel, a spring device supported on saidsteering column assembly, said device having a rotatably mounted shaftspaced from said steering shaft, a spiral leaf spring having one endconnected to said second-mentioned shaft, the other end of said springbeing anchored on said steering column assembly, a spool connected tosaid second-mentioned shaft, flexible connecting means interconnectingsaid spool and said steering shaft whereby when said steering shaft isrotated a spring force is transmitted from said spiral leaf springthrough said flexible connecting means to said steering shaft tending tourge said steering shaft to its central neutral position, said springdevice exerting a force on said steering shaft when said steering shaftis turned to a nonneutral position that exceeds any reaction forceoccurring in said steering gear.